As far as I can see, you load that card with CAD and then change it to the currency that you want. However, when you convert that CAD to USD in your card's wallet, it's converted at an exchange rate which isn't disclosed, but I would bet us 2.5%-3.0% higher than the actual exchange rate. So, there is no real benefit to using that card vs. your Canadian card.
The best option to avoid fees is to use a Canadian card that doesn't charge you a foreign transaction fee (FTF). There are only a few cards in Canada that fit the bill, including: 1) any Brim MC; 2) HSBC World Elite MC; 3) Scotia Passport Visa Infinite; and 4) Scotia Gold Amex. All of those cards do NOT charge you a FTF, AND they also give you rewards on top of that.
There are also other cards that don't charge the FTF but also don't give you rewards (e.g., Home Trust Visa), and there are also a few cards that charge you the FTF but provide rewards to just offset it, or marginally higher (e.g., MBNA
Amazon Visa, Rogers World Elite MC).
Using any of these cards will give you the best exchange rate you can get at any given time. If you want to speculate on currency movements, and buy USD "when the rate is good" and keep it in your USD account, then you could also consider a Canadian USD card, but those cards don't provide any rewards, and when you buy USD when you think "the rate is good", you are still paying a FTF to buy that USD. Unless of course you have USD income/assets, or have a very cost effective way to purchase USD, which some do.